The present invention relates to a device for the fermentation of drinks containing sugar and in particular the preparation of sparkling wine such as champagne by a second fermentation, or refermentation of a still wine in the bottle.
The traditional so-called "champagne" method consists of adding a "liqueur de tirage" containing sugar and the fermentation yeast necessary for the conversion of the sugar into carbon dioxide to still ordinary wine, which has already undergone a first alcohol fermentation. Bottling may be carried out before or after these additional stages.
The bottles are then corked using a hollow plastic stopper inserted into the neck of the bottle and sealed by crimping a metal cap. They are then generally stored horizontally "on slats" for a long period of time lasting from several months to several years in cellars where the temperature is kept constant, generally between 10.degree. and 15.degree. C. so that fermentation takes place with a corresponding rise in pressure or "bottle fermentation" in the bottles.
At the end of this long fermentation period, each bottle must be shaken individually several times in order to dislodge the fermentation deposit which might stick to the walls of the bottle. During this shaking period the bottles are also inclined then stored "on the point", that is to say inclined with the neck downwards, to facilitate the decanting of the yeasts and encourage the fermentation waste products to be deposited inside the hollow plastic stopper situated in the neck of the bottle.
Once shaking is completed, the bottles are transported vertically, with the neck downwards, and are plunged in a refrigeration brine bath maintained at about -20.degree. C. in order to form, by freezing, a plug of frozen wine containing the fermentation yeast waste products.
The bottles then undergo a disgorging operation which consists of vertically placing the bottles with the thus frozen neck upwards and of decapping them, which causes, under the action of the pressure inside the bottle, the ejection of the plastic stopper together with the frozen plug containing the fermentation sediments.
The original level of the bottles is then restored by the addition of a "liqueur d'expedition" and the bottle is sealed with a permanent stopper which is generally made of cork.
The traditional so-called "champagne" method that has just been described requires significant manual labor, in particular after fermentation when the bottles are shaken, an act often carried out by hand. This method also involves a large surface area for storing the bottles on special racks and a rather long storage time which may be more than one month. In addition, the traditional method includes a stage of freezing the neck of the bottles, which is indispensable for the elimination of the yeasts.
Attempts have been made to try to remedy these drawbacks.
U.S. Pat. No. 4,792,454 assigned to Millipore Corporation, the parent company of the assignee of this application, describes a process for fermenting wine in the bottle according to the champagne method. This prior art process includes the introduction of a tubular filter cartridge into the neck of the bottle of wine which has had added to it the quantity of sugar necessary to obtain the desired final pressure of carbon dioxide. This cartridge has a perforated tubular body, externally coated with a hydrophilic filter membrane and a hydrophobic filter membrane and contains the yeasts necessary for the fermentation of wines containing sugar with release of carbon dioxide. The use of such a filter cartridge has the advantage of eliminating the need for a shaking stage which allowed the deposit of yeasts to be concentrated in the neck of the bottle, as well as the requirement of freezing the neck of the bottle, which allowed the plug containing the yeast residues to be frozen and ejected, since the yeasts are no longer in contact with the inside of the bottle. The technique described in this U.S. patent does, however, have certain drawbacks.
In fact, it has been observed that the rise in pressure of the carbon dioxide in wine bottles fitted with a cartridge according to the teachings of U.S. Pat. No. 4,792,454 required a longer time than that necessary for fermentation according to the traditional champagne method. Such an increase in the duration of bottle fermentation results in an unacceptable modification of the organoleptic properties of the wine which has undergone a second fermentation under these conditions.
Furthermore, during experiments carried out to identify the mechanisms involved during bottle fermentation according to the aforementioned U.S. patent, it was noted that the cartridge, filled with yeast and immersed in wine, quickly emptied itself of any liquid under the pressure of the carbon dioxide produced by the yeast. The gas thus accumulated inside the cartridge only escaped (in the form of bubbles) through the vent, constituted by the hydrophobic membrane, when the pressure was sufficient to overcome the forces of surface tension. This filter cartridge therefore acts as a surface fermentor, in which only the yeasts in contact with the hydrophilic membrane are wetted by the wine and can therefore live and consume the sugar.
Furthermore, during the fermentation reaction, the yeasts which consume the sugar while producing mainly ethanol and carbon dioxide release energy in the form of heat. Hence the wine in contact with the yeasts is depleted of sugar and simultaneously its temperature is raised slightly by the fermentation reaction, and then it is replaced due to thermal convection by wine which is colder and richer in sugar. In addition, the structure itself of the cartridge described in the U.S. patent mentioned above, where the surface of the membrane lined on the inside with yeasts acts as a heat generator, limits the convection currents due to its cylindrical shape and its bulkiness in the neck of the bottle.
The fabrication of hollow fiber membrane devices is well known in the art. To make an effective separation device, the hollow fibers must be potted or bonded together at one end, inserted into a housing and sealed therein to obtain a fluid-tight barrier between the inside and the outside of the fibers. Conventionally, the hollow fibers are bundled together and potted at one end (or both ends as the case may be) with an adhesive, such as an epoxy glue or polyurethane. In a second step, the bundled fibers are sealed in an appropriate housing. The use of polyurethane or epoxy adhesives typically involves the use of a centrifuge to assist the adhesive to flow around and between each fiber to assure an adequate seal.
Conventional potting technology suffers frown several disadvantages in addition to the use of centrifugation to overcome viscosity effects. First, the use of adhesives requires a long time to reach complete polymerization, a fact which burdens the overall manufacturing process as there exists a significant amount of residence time before the adhesive becomes hard enough to cut the potted end to expose the lumens of the fibers. Second, these adhesives are a persistent source of organic extractable contaminants as well as particulate matter resulting frown shedding due to the gradual hydrolysis and deterioration of the adhesive. In addition, such adhesives have a tendency to wick up the fibers and wicking can lead to fiber breakage upon physical stress or fatigue.
To overcome these disadvantages, it has also been proposed to utilize thermoplastic resins to join and form the seal around the hollow fibers to create a usable fiber bundle. Such resins may either be pure polymers or can contain adhesive additives which are chemically compatible with the thermoplastic polymer to avoid the aforementioned extractable contaminant/particulate matter problems.
U.S. Pat. No. 5,015,585 (Robinson) describes a process for making a homopolymer hollow fiber module by thermal bonding techniques which first requires insertion of a metal rod into the lumen of each hollow fiber to maintain its shape and integrity during the bonding process. These strengthened hollow fibers are conventionally potted by immersing the fibers into a mold containing a suitable molten thermoplastic. Using this technique, the spaces between the hollow fibers are filled or otherwise melted while keeping the lumens of the fibers open. After bonding is completed, the rods inserted into the fibers are forced through the ends and removed; this is followed by cutting the bundle end to create a through hole for communicating with the interior of the fiber lumen. While Robinson suggests that any thermoplastic polymer can be used to produce a homopolymer module, the disadvantage with this technique is the difficulty in reliably and efficiently inserting a rod into each hollow fiber.
U.S. Pat. Nos. 4,980,060 and 5,066,397 (Muto et al) disclose another process for thermoplastically sealing the ends of a hollow fiber filtration module by first dipping the fiber ends into an inorganic cement (e.g. gypsum) thereby filling a portion of the lumens and allowing it to set. A bundle of fibers is then gathered and the filled ends are potted using a molten thermoplastic resin. Alternatively, the filled ends may be directly fusion bonded together to form the requisite seal. The bonding step is followed by conventionally cutting of the ends and finally dissolving the cement inside the lumen ends with a suitable chemical. This technique is not universally applicable since inorganic cements must be found that do not damage the membrane either by themselves or by the solvent required for their removal. Finally, this technique is undesirable due to the difficulty of the steps involved as well as the potential contamination resulting from the inorganic cement which may not totally be removed.
U.S. Pat. No. 5,228,992 (Degen) discloses a process for enhancing the ends of thermoplastic hollow fibers, e.g. by radiation cross-linking, in order to increase the fiber's ability to withstand the high temperature inherent in injection molding techniques. The ends are subsequently potted by a conventional molding technique. The difficulty with Degen's process is that the fibers have to be specially treated at the ends to render them more stable at high temperatures. Furthermore, cross-linking is not suitable for some polymers, for example fluoropolymers.
All of the aforementioned techniques require a special treatment of the ends of the hollow fibers to render them resistant to the high temperatures necessary to pot the bundle, temperatures so high that the fiber would normally collapse or otherwise completely melt. Additionally, these techniques require that the fiber be processed as single entities rather than as a grouped array. Furthermore, the bundled fibers must then be sealed as part of a further manufacturing step in a suitable housing.
Other processes have been devised which focus on producing a more uniform bundle. U.S. Pat. No. 5,186,832 (Mancusi et al) discloses a method for producing a uniform bundle by first converting the hollow fibers into a fabric with the fibers transversely oriented, in a spaced-apart, mutually parallel relationship and held in place by warp filaments. The device is assembled by spirally winding the fabric made out of hollow fibers to obtain a uniformly-spaced fiber bundle. In this process the fiber bundle is sealed using conventional resinous potting material. In addition to conventional potting methods, this patent discloses a technique for simultaneously applying resinous potting material to the ends of the bundle as the woven fabric is wound rather than subsequently potting the bundle after winding. However, no mention is made of sealing the fiber ends with a molten thermoplastic polymer. Thus the use of adhesive resins in the process taught by the '832 patent suffers from all the disadvantages mentioned above. In addition, this technique involves multiple steps prior to fabricating a finished hollow fiber membrane module.
More recently, U.S. Pat. No. 5,284,584 (Huang et a) discloses techniques for fabricating an all thermoplastic, spirally wound hollow fiber membrane cartridge. Like the Mancusi et al patent (U.S. Pat. No. 5,186,832), Huang et al teaches first preparing a fabric array with transversely oriented warp filaments used to create a uniform spaced-apart bundle of mutually parallel fibers and then bonding in a second step the bundle within a housing. Thus this patent suffers from the same disadvantages in this regard as discussed with respect to Mancusi et al. While this patent teaches that the temperature of the molten resin at the point of contact with the hollow fiber must be lower than the melting point of the fiber, there is no disclosure of bonding the fibers together directly within the housing in one, relatively simple process step.
Thus despite numerous prior attempts, there still exists a need for improvements in the art of designing and efficiently manufacturing a reliable hollow fiber membrane module which is both chemically and mechanically robust and which has essentially no possibility of shedding undesired particulate contaminants or producing other extractables, the manufacture of which may be accomplished in a minimum number of manufacturing steps.